The overall goal of this application is to determine the mechanisms by which heat shock protein 90 (Hsp9O) mediates endothelial nitric oxide synthase (eNOS) function to direct endothelial biology and vascular physiology. Recent reports from this laboratory demonstrate that eNOS is fully capable of generating both nitric oxide (.NO) and superoxide anion (O2-). When conformational changes in Hsp9O are blocked with geldanamycin (GA) eNOS generates O2- upon activation. When endothelial cultures and isolated pressurized microvessels are pre-treated with angiostatin they also appear to generate O2 about by an eNOS-dependent mechanism to shift the balance from .NO towards O2 about which impairs vasodilation. These data suggest that Hsp90 interactions direct which radical species is generated by eNOS. Both angiostatin and GA induce altered states of eNOS activation as defined by the levels of phospho-eNOS (S1179) on eNOS and Hsp90 associated with eNOS. Additional studies aimed at determining the phosphorylation state of eNOS suggest that Hsp90 interactions with eNOS may protect or promote serine phosphorylation at another site on eNOS. As the presence of phosphoserine on eNOS inversely correlates with O2 about this site may influence the function of eNOS by directing radical species generation. The signal transduction mechanisms governing Hsp90 interactions with eNOS with respect to O2 about generation remain unknown. As the balance of .NO and O2 about in the endothelium mediate many functions, endothelial proliferation and vasodilation, understanding how angiostatin and GA alter signaling pathways governing eNOS function is central to understanding the mechanisms governing angiogenesis for developing new collatoral vessels and increasing vasodilation to prevent ischemic heart disease. Findings from these studies will probably be relevant to and provide new understanding of mechanisms mediating vascular disease related to atherogenesis, hypertension and diabetes